This research project is comprised of a related set of studies of diagnostic technology that have three overall objectives: (1) evaluation of the clinical efficacy, costs, and cost-effectiveness of selected diagnostic tests and technologies; (2) better understanding of the development and diffusion of medical technology; and (3) improved use of available diagnostic tests and technologies. The technologies investigated in the study include laboratory devices and procedures (automated clinical chemistry analyzers and automated white blood cell differential counters), imaging tests (computed tomography and ultrasound of the pancreas and chest X-rays), and a physiologic function test (long-term electrocardiography). The methods used in these projects are diverse and reflect the variety of research objectives being pursued. Our studies of diffusion employ literature reviews, market surveys, interviews and analysis of available data on the spread of laboratory tests and equipment. Studies of the information provided by imaging tests entail interpreting images under controlled conditions of observation and developing and applying improved methods of analysis. Studies of cost and cost-effectiveness require design of assessment models and extensive accumulation of data from laboratories and (in the case of long-term electrocardiography) from community physicians and patients. Diagnostic technologies as a class raise particular methodologic issues in the evaluation of efficacy, cost and cost-effectiveness. Our aim is both to perform the analyses for the specific technologies described and to establish analytic models applicable as well to other diagnostic tests and technologies.